The phenomenon, which is rarely created in laboratory conditions, shows a less intuitive side of Newton’s Second Law of Motion, in which a force is equal to the mass of an object times its acceleration (F=ma).

Our everyday world sees only the positive effect of the law: if you push an object, it moves away from you.

“That’s what most things that we’re used to do,” said Michael Forbes, a WSU assistant professor of physics and astronomy and an affiliate assistant professor at the University of Washington. “With negative mass, if you push something, it accelerates toward you.”

First predicted theoretically by Satyendra Nath Bose and Albert Einstein, a Bose-Einstein condensate is a group of atoms cooled to such a low temperature that there is hardly any movement left in the group. At that point, the atoms begin to clump together becoming identical, from a physical point of view, and the whole group starts behaving as though it were a single atom.

Once scientists reached that stage, they used lasers to kick atoms back and forth until they started spinning backwards. When the rubidium rushes out fast enough, if behaves as if it had negative mass.

“Once you push, it accelerates backwards,” said Mr Forbes, who acted as a theorist analysing the system. “It looks like the rubidium hits an invisible wall.”

The physicist explained that the ground-breaking aspect of their research is the "exquisite control" they have of the negative mass using their technique.

The heightened control gives researchers a new tool to engineer experiments to study similar behaviours in astrophysics, such as neutron stars, and cosmological phenomena like black holes and dark energy, where experiments are impossible.

“It provides another environment to study a fundamental phenomenon that is very peculiar,” Mr Forbes said.